制冷技术第四章.docx

Part 2. The Principles of Refrigeration ( 80-90 pages) 第二部分.制冷原理Chapter 4. Methods of Decreasing Temperature ( II ) Relative to solid refrigerants第四章•降温方法相对于固体制冷剂李增扬4-1 Decreasing temperature by Thermo-Electric Peltier Effect4-1 Peltier热电效应降温法1. Thermo-electric refrigeration1.热电制冷In 1834 J. Peltier discovered that when an electric current passes around a circuit composed of two different metals， one junction became cool and the other became warm. Peltier effect is the converse of the Seebeck effect. If two different metals (or a metal and a semiconductor) are joined and the two junctions are kept at different temperatures, an electromotive force (e.m.f.) is developed in the circuit. This is Seebeck effect, and the circuit constitutes a thermocouple.1843 J. Peltier发现当电流通过有两种不同金属组成的电路时，一端会变冷一端会变热。

Peltier 效应与Seebeck效应正相反如果两种不同的金属(比如一种金属和一种半导体)接在一起，并且 两个接点保持在两个不同的温度，电路中会产生热电势这是Seebeck效应，并且线圈由热电偶组 成Thermo-electric refrigeration works on the principle of the Peltier effect. The effect is reversible, i.e. reversing the current cause the cold junction to become hot，and the hot junction to cool. Larger temperature differences are produced with metal-semiconductor junctions than with metal-metal junctions. An n-type semiconductor produces a temperature difference in the opposite sense to a p-type semiconductor. A Peltier element consists of a number of such junctions in series, with n-type and p-type semiconductor alternating.热电制冷的工作原理是Peltier效应。

Peltier效应是可逆的，也就是说电流的颠倒引起冷触点变 热，热触电变冷金属-半导体的触点比金属-金属触点产生更大的温差相对于P型半导体，N型 半导体可以产生一个温差Peltier效应的一个要素是大量分级N-P轮流的触点The principle of thermo-electric refrigeration is shown in Fig.4-1. Two rods of dissimilar materials, A and B, are joined to a metal plate which accomplishes the cooling duty at temperature T .There is a ccold heat exchanger at low temperature T , to absorb heat Q from the object to be cooled. The other ends of the rods A and B are separately placed in thermal contact with a hot heat exchanger at temperature T , and also electrically connected to the poles of a direct current power supply. If a current I is passed round the circuit, the cold junction will absorb heat Q at temperature T , and reject heat Q at temperature T .H图4-1所示是热电制冷的制冷原理。

两段不同的材料A和B连接到一个金属板来完成制冷，温 度降低到Tc有一个温度为Tc的冷却换热器，用来吸收来自被冷却物体的热量Qc，AB的另一端 分别与温度为T的高温换热器和电力驱动的直流电源相接如果线圈中通过电流I，冷触点将在 H温度Tc下吸收热量Qc，并在温度Th下释放热量QhD.C. PowerHeat sourceNegative (—)Heat sink (hot sid e)Th 已 rmo 已 1 ectric module configuration(ceramic)Fig.4-1, The Principle of thermo-electric refrigeration 图4-1，热电制冷原理日已 miconductorElectricalconductor (copper)A practical thermoelectric cooler usually consists of several modules of semiconductor material that are connected electrically in series and thermally in parallel. There is no compressor and no fluid flow involved. The thermoelectric cooler has the advantages of being compact, simple, quiet, and reliable. Its refrigerating capacity can be simply controlled by input voltage of DC power. However the efficiency ofthe thermaoelectric refrigeration is quite low compared with vapor compression refrigeration. Up to now the applications of thermal-electric refrigeration are mainly found in special situations where require small refrigeration load in restricted space, for example, Calorie meter, CPU cooler, cold water machine, dehumidifier, refrigerators of drugs, beer, cosmetics, mini-refrigerator for vehicle, mini-coolers for laser and infrared equipment and sensors, electronic switch board cooling and aviation black box cooling, and many other instruments. Future applications of thermal-electric refrigeration will mainly depend on the new development of thermal-electric materials, which will be shown later in this section.实际的热电制冷机通常由几个在电气上串联在热力上并联的半导体模块组成。

其中并没有压缩 机和流体流动热电制冷机有紧凑，简单，安静和可靠的优点其制冷量可以简单的通过控制输入 的交流电流来控制然而，热电制冷的效率比蒸汽压缩机的效率相比小很多迄今热电制冷的应用 主要用于在有限空间低制冷负荷的特殊情况，比如说：量热器，CPU冷却器，冷水机器，干燥器， 药物，啤酒，化妆品的制冷机，小型载体的制冷，小型激光的制冷，红外仪器和感受器的制冷，电 力控制板的冷却和航空黑匣子的冷却，还有很多其他仪器热电制冷的进一步应用取决于热电材料 的新发展，这些将在本章介绍2. Analysis of thermo-Electric refrigeration [13 ]2.热电制冷的分析[13 ]The quantity of heat is directly proportional to the current in the circuit: 热量和线圈中的电流大小成正比，有：(4-1)(4-2)Q = •兀 x Iand 兀=a x TWhere 兀 is called Peltier coefficient, 这里兀叫做Peltier系数， and a is thermoelectric power, also called differential Seebeck coefficient.a为温差电动势，也叫微分Seebeck系数.T is the temperature of the junction, KT是触点处的温度，K(4-3)The heat absorbed per unit time by Peltier coefficient at the cold junction is 单位时间内冷触点Peltier系数吸收的热量为： Qp =a x I x TThe heat produced by electric resistance of the thermo-electric elements, Joule heat, is 由热电元件电阻产生的热量是QJ = 12 xR/2 (4-4)Where assuming half of the joule heat is added to the cold junction; 这里假设焦耳热的一半是加到了冷触点上and R is the resistance of the thermo-electric element, in ohm, Q . 并且R是热电元件的电阻，单位为Q。

The heat transfer from the hot junction to cold junction by thermal conduction can be quantified asfollows。